Python Compare Strings [10+ Examples]

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Introduction to Python compare strings

In python, everything that we write inside double or single quotation marks is treated as a string. Strings are immutable sequences of data type and strings are actually a sequence of Unicode characters. In this tutorial, we will talk about python string comparisons. We will take different cases and see how we can compare strings by taking examples using different comparison operators. Moreover, we will also compare strings in the list as well. By the end of this tutorial, you will have a solid knowledge of python compare strings.

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Example of Python strings

As we already discussed, that string is an immutable sequence data type which is wrapped inside single, double, or triple quotes.

See the example below:

# creating string
x = "My name"

# printing type
print(type(x))

Output:

<class 'str'>

A white space written inside quotation marks is also considered to be a string type. See the example below:

# creating string
x = " "

# printing type
print(type(x))<code>

Output:

<class 'str'>

 

Python compare strings ignore cases

Now let us compare two strings in python. In this particular section we will develop a python program to compare between strings to ignore cases or case-sensitive. Python is a case sensitive programming language. Here uppercase letter is not equal to a lowercase letter. That means when we compare two strings in python they should be exactly the same, even the case otherwise they will be considered to be different. See the example below:

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str1 = "Hello"
str2 = "hello"

print(str1==str2)

Output:

False

However, we can develop a case-insensitive program which means that it will ignore the uppercase or lowercase differences.

 

Python compare strings ignore case using lower function

In Python there is a built-in function known as lower() function which converts all the uppercase characters in a string to a lowercase character. See the example of how we can ignore the case sensitivity using a lower function.

str1 = "Hello"
str2 = "hello"

print(str1.lower()==str2.lower())

Output:

True

 

Notice that this time we get True because lower() function converts all the characters into lower case and then compares the two strings.

See one more example here which compares.

# strings
str1 = "My name Is Bashir alam"
str2 = "my name is bashir alam"

# if statement to compare two strings
if str1.lower() == str2.lower():
   print("they are same")
else:
   print("they are not same")

Output:

they are same

 

Python compare strings ignore case using upper method

We also have a built-in function known as upper() which converts all the lower case characters to upper case. It works in a similar way we lower works. See the example below:

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# strings
str1 = "Hello"
str2 = "hello"

# check using upper function
print(str1.upper()==str2.upper())

Output:

True

In a similar way, we can use them in if-else statements as well. See one more example below:

# strings
str1 = "My name Is Bashir alam"
str2 = "my name is bashir alam"

# if statement to compare two strings
if str1.upper() == str2.upper():
   print("they are same")
else:
   print("they are not same")

Output:

they are same

 

Python compare strings ignore case using casefold function

The casefold function is another python built-in function that works similar to lower and upper methods. But unlike lower() and upper() which performs a strict string comparison by removing all the case distinctions, the casefold method is used for caseless matching. For example the german letter ß is equal to ss in english. If we apply an upper or lower method to compare this character with ss, it will return False, but the casefold will convert ß to ss and return True. See the following example.

# strings
str1 = "ß"
str2 = "ss"

# check using upper function
print(str1.casefold()==str2.casefold())

Output:

True

 

Python compare two strings characters by characters

Another way to compare two strings is to compare character by character. As we know strings are iterable so we can iterate over them and compare each character. There can be many ways to iterate but here we will see the simplest one. See the example below which used for loop to iterate over string and compares both:

# function to compare two strings
def stringCompare(str1, str2):

   # for loop to iterate
   for i in range(len(str1)):

       # check each characters
       if str1[i]!=str2[i]:

           # return false is one of the character is not equal
           return False
       else:
           pass

   # if all characters are equal, it returns true
   return True

print(stringCompare("my name is bashir alam", "my name is bashir alam"))

Output:

True

In the above example, the function takes two strings as an input and uses a for loop and then compares each character of strings by specifying their index number.

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In a similar way we can compare character by character by ignoring the case difference. See the example which ignores the case difference.

# function to compare two strings
def stringCompare(str1, str2):

   # for loop to iterate
   for i in range(len(str1)):

       # check each characters
       if str1[i].lower()!=str2[i].lower():

           # return false is one of the character is not equal
           return False
       else:
           pass

   # if all characters are equal, it returns true
   return True

print(stringCompare("My NamE is BAshir ALam", "my name is bashir alam"))

Output:

True

We still get True because the lower() method converts all the upper case into lowercase and then compares the characters.

 

Python compare strings and return the difference

There might be a situation where we wanted to find out the difference between two strings, or we wanted to compare two strings but it returns False so we wanted to figured out the difference between those two. In python there can be many ways to achieve this but here we will take the most simplest one. See the following code.

# function to print the difference
def compareString(str1, str2):

   # creating empty variables
   result1 = ''
   result2 = ''

   #handle the case where one string is longer than the other
   maxlen=len(str2) if len(str1)<len(str2) else len(str1)

   #loop through the characters
   for i in range(maxlen):
       #use a slice rather than index in case one string longer than other
       letter1=str1[i:i+1]
       letter2=str2[i:i+1]

       #create string with differences
       if letter1 != letter2:

           # adding letters to result
           result1+=letter1
           result2+=letter2

   # printing the difference
   print ("Letters different in str1: ",result1)
   print ("Letters different in str2: ",result2)

# calling the function
compareString("Bashir", 'bashir')

Output:

Letters different in str1:  B
Letters different in str2:  b

Notice that in the given string only the B was different and this program successfully returns the different value.  Here is another way of applying the same logic. See the code below which returns the difference values.

# function to print the difference
def compareString(str1, str2):
   # creating empty strings
   result1 = ""
   result2 = ""

   # looping str1 and str2
   for a, b in zip(str1, str2):

       # check if equal or not
       if a != b:
           result1+=a
           result2+=b
   return result1 +"  and  " +result2

# calling the function
print(compareString("Bashir", 'bAshir'))

Output:

Ba  and  bA

As we mentioned earlier, there can be many more methods to achieve the same result. You can choose any of them depending on your coding skills.

 

Python compare strings ignore whitespaces

Now let's see the following simple example where we will try to compare two strings, one with whitespace before it and one without any white space.  See the example below:

# strings
str1 = "B"
str2 = " B"

# compare two strings
print(str1==str2)

Output:

False

We get False because whitespaces are also considered to be characters in python. Suppose we don't want our program to consider whitespaces, in python we can achieve this by a simple piece of code. Python provides us a built-in function known as strip() which helps us to achieve the above-mentioned logic and it ignores the white spaces.

# strings
str1 = "B"
str2 = " B"

# compare two strings using strip function
print(str2.strip() == str1.strip())

Output:

True

This time it returns True because the strip function ignores the whitespaces and then we compare the strings.

See one more example which contains a lot of white spaces.

# strings
str1 = "This is Bashir Alam"
str2 = "        This is Bashir Alam"

# compare two strings using strip function
if str1.strip()==str2.strip():
   print("both are same")
else:
   print("Both are different")

Output:

both are same

 

Python compare strings not equal operator

So far we have compared the strings using python equality sign ( == ). However, python also supports us to compare strings based on not equality sign (!=). This will return true if both of the strings are not equal otherwise it will return False. See the example below:

# strings
str1 = "Bashir"
str2 = "Alam"

# compare strings
print(str1!=str2)

Output:

True

It returns True because both of the strings are not equal and our assumption is True.

In Python is not is also an alternative to compare two strings. It will also return True if both the strings are not the same.  See the example which uses is not instead of != operator

# strings
str1 = "Bashir"
str2 = "Alam"

# compare strings
print(str1 is not str2)

Output:

True

 

Python compare strings with wildcard

The asterisk (*) is used to specify any number of characters. It is typically used at the end of a root word. This is great when you want to search for variable endings of a root word. For example, searching for clean* would tell the database to look at all the possible words ending to root clean. Result might be cleaning, cleaner or cleaned depending on our list of words.

While question mark (?) is used to represent a single character anywhere in the word. It is most useful when there are variable spellings for a word, and we want to search for all variants at once. For example, searching for l?st might return list or lost depending on the words available.

 

Now let us take an example of both asterisk and question mark to search for different words. See the python code below:

# Regular expression library
import re

# list of different words
WordList = ["list", "clean", "lost","cleaner"
          , "worker", "working"]

# for loop to iterate our list of words
for word in WordList:

       # The . symbol is used in place of ? symbol
       if re.search('l.st', word) :

           # printing the word
               print (word)

Output:

list
lost

Now let us take the example of asterisk and see what we get for clean*. See the example below:

# Regular expression library
import re

# list of different words
WordList = ["list", "clean", "lost","cleaner"
           , "worker", "working"]

# for loop to iterate our list of words
for word in WordList:
       # The .+ symbol is used in place of * symbol
       if re.search('clean.+', word) :

           # printing the word
           print (word)

Output:

cleaner

 

Python compare strings in a list

Python provides us various ways to compare two lists. Comparison is the process when the data items of one side are checked against another data item to see whether they are the same or not. Here we will compare the data of two sets and see if they are equal or not.

See the example below which direct equality sign to compare two lists containing strings as a data set.

# lists containing strings
list1 = ["a", "b", "c", "d"]
list2 = ["a", "b", "c", "d"] 

# compares two lists
if list1 == list2: 
   print("The list1 and list2 are equal") 
else: 
   print("The list1 and list2 are not equal")

Output:

The list1 and list2 are equal

Suppose we want to compare two sets and we assume that it should return True for duplicates values as well. We can achieve this by using the set() method, which will first convert our list to set and delete any duplicate elements. See the example below:

# lists containing strings
list1 = ["a", "b", "c", "d", "d"]
list2 = ["a", "b", "c", "d"] 

# compares two lists
if set(list1) == set(list2): 
   print("The list1 and list2 are equal") 
else: 
   print("The list1 and list2 are not equal")

Output:

The list1 and list2 are equal

Notice that list1 contains duplicates elements but still we get True for comparison because set() method removed the duplicate values.

Another method of comparing two sets of strings might be to loop over them and compare each element and if they return True if all are the same. See the python program below which compares the list of strings using for loop.

# function to compare list
def compareList(str1, str2):

   # for loop to iterate
   for i in range(len(str1)):

       # check if data is not equal
       if str1[i]!=str2[i]:

           # return False
           return False
       else:
           pass

   # return True
   return True

# calling the function
print(compareList(["a", "b", "c", "d"] ,["a", "b", "c", "d"] ))

Output:

True

 

Python compare strings lexicographically

We use comparison operators to compare strings lexicographically in Python. We already have used equal and not equal operators to compare strings. Here is a list of comparison operators that are used to compare two strings.

  • Equal to == : check if two strings are equal
  • Not equal to !=: check if two strings are not equal
  • Greater then > : check if a string is greater than other
  • Less than < : check if a string is less than other

As we already have used the first two operators, in this section we will focus on the last two comparison operators. See the following example which compares two strings.

# strings
str1 = "B"
str2 = "b"

# comparing
print(str1 > str2)
print(str2 > str1)

Output:

False
True

Notice that the upper case B is smaller than the lower case b because in the ASCII  set, the numeric value of upper B is 66 while that of lower one is 98. In python all the uppercase alphabets have smaller numeric values ( starting from 65 ) and all the lower case alphabets have larger numeric values ( starting from 97).

See the example below which uses less than operator. This time it will return True for uppercase letters.

# strings
str1 = "B"
str2 = "b"

# comparing
print(str1 < str2)
print(str2 < str1)

Output:

True
False

Now let us compare two lists containing strings dataset. See the example below:

# strings
str1 = ["bashir", "alam"]
str2 = ["bashir", "Alam"]

# comparing
print(str1 < str2)
print(str2 < str1)

Output:

False
True

 

Summary

Strings are sequences of characters that can include numbers, letters, symbols and whitespaces. Everything in python that is written inside single, double or triple quotation marks will be considered as string.  Python strings are an important data type because they allow us to interact with text-based data in our programs. In this tutorial we learned about string comparison. We covered various ways to compare strings in python using different comparison operators and examples.

 

Further Reading Section

python compare strings
Python string
comparison operators

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